Coral reefs are packed with thousands of underwater species. Scientists say that reefs might contain more different species of animals than rain forests; in fact, even the coral itself is a living organism! The species that live together on or in a reef make up their own ecosystem, which means they depend on each other for survival.
The two main reasons that sea creatures live in (or around) reefs are food and shelter. They can all be categorized into groups by size and where exactly they fit in the reef's ecosystem.
Plankton are some of the tiniest reef-dwellers. They float around aimlessly and usually become food for bigger sea creatures.
Bottom-dwelling creatures, like sponges, anemone, and star fish call coral reefs home. They can attach themselves to a reef's surface and find food and nutrients easily. Shrimp, sea urchins, and sea cucumbers can move around the reef easily and take shelter in it's holey surface.
The water around coral reefs is very warm, so swimmers that need a balmy temperature to survive usually live on or around them. Both sea horses (who can change their colors to match the coral) and clown fish (who depend on reef-dwelling anemones for protection) rarely venture past a reef's borders.
Sea animals with shells, like turtles, love hanging around coral reefs. There's plenty of delicious algae for vegetarian turtles, and lots of little crustaceans and jellyfish to snack on for meat-eaters. The tops of reefs are usually pretty close to the surface, which is perfect for turtles who need to come up for air. Crabs love them, too - although sometimes they're turtle food.
Conchs, famous for their beautiful, tropical-looking shells, also find a lot of food in reefs - they eat algae, grasses, and other floating vegetation. Clams, oysters and scallops also enjoy the benefits of living on a reef - there's an all-you-can-eat buffet and plenty of places to hide.
Rays and eels also live in coral reef areas. While the rays can glide gracefully above, eels can play hide and seek with one another (and their prey) in the reef's holey surface. Octopus, squid, and jellyfish share the same living space with these animals, too.
Many species of sharks call coral reefs home, too - there's plenty of smaller fish to eat and the warm waters give them the fuel necessary for hunting. Even whales visit reefs frequently; some of them eat the plentiful zooplankton, while others eat bigger (but still little, compared to them) fish.
There are also dozens of plants that live among the coral, providing food and shelter for the reef's inhabitants. The plants play an important role for each species - without them, the delicate balance of the reef's ecosystem would be thrown off, causing utter chaos in the deep blue.
With thousands of creatures depending on the reef for food and shelter, it's impossible to list each one individually. It's important to remember that reefs develop in warm, sunny waters and plenty of plant life is needed to sustain them. By grouping the types of animals that live on a reef together, it's easy to determine which animals would be well-suited to reef life and which would not.